I don't think any colors are disallowed, they are just really picky about how they want the colors to show. Not too much, not to little...not sure of the why, but here's the AKC's outline:

Quote:

Color, Markings and Patterns
Brindle--The base color shall be yellow gold and always brindled with strong black cross stripes in a chevron pattern. A black mask is preferred. Black should appear on the eye rims and eyebrows, and may appear on the ears and tail tip. The more intensive the base color and the more distinct and even the brindling, the more preferred will be the color. Too much or too little brindling are equally undesirable. White markings at the chest and toes, black-fronted, dirty colored brindles are not desirable.
Fawn--The color shall be yellow gold with a black mask. Black should appear on the eye rims and eyebrows, and may appear on the ears and tail tip. The deep yellow gold must always be given the preference. White markings at the chest and toes, black-fronted dirty colored fawns are not desirable.
Blue--The color shall be a pure steel blue. White markings at the chest and toes are not desirable.
Black--The color shall be a glossy black. White markings at the chest and toes are not desirable.
Harlequin--Base color shall be pure white with black torn patches irregularly and well distributed over the entire body; a pure white neck is preferred. Merle patches are normal. No patch should be so large that it appears to be a blanket.
Eligible, but less desirable, are black hairs showing through the white base coat which give a salt and pepper or dirty appearance.
Mantle--The color shall be black and white with a solid black blanket extending over the body; black skull with white muzzle; white blaze is optional; whole white collar is preferred; a white chest; white on part or whole of forelegs and hind legs; white tipped black tail. A small white marking in the blanket is acceptable, as is a break in the white collar.

Any variance in color or markings as described above shall be faulted to the extent of the deviation. Any Great Dane which does not fall within the above color classifications must be disqualified.

My understanding is its simply for tradition reasons. Same reason you wouldn’t allow a mismark dally in the breed ring or a mismark dobe or rottie etc... IDK. And yes, mismarks do occur in responsible breeding programs.

Now, not allowing merle is historically related to health issues. Breeders believed merles (nor harles) were the ones who caused deafness so they were removed from the gene pool and in fact used to be bucketed Now that we know more about genetics, in europe they have started allowing merles to be shown. I don’t see that happening any time soon in the AKC, they only just let mantles in the breed ring!

ETA:
In Germany HarleXHarle, MerleXMerle and HarleXMerle breedings are not allowed and if you are caught you will be heavily fined.

__________________

"We become better trainers by refusing to swallow uncritically what is tossed to us as truth,
by developing our powers of empathy and observation,
and by searching for better ways to teach and educate the dogs we love."

I don't think any colors are disallowed, they are just really picky about how they want the colors to show. Not too much, not to little...not sure of the why, but here's the AKC's outline:

"Any Great Dane which does not fall within the above color classifications must be disqualified." I think Red was asking about things like blue brindle, blue fawn, harlequin with fawn, brindle, blue, etc patches. All are technically genetically possible if breeders choose to go outside of the color breeding "rules" but none are showable.

I don't know why, other than apparently GD breeders collectively decided they didn't like those colors/patterns in their breed.

"Any Great Dane which does not fall within the above color classifications must be disqualified." I think Red was asking about things like blue brindle, blue fawn, harlequin with fawn, brindle, blue, etc patches. All are technically genetically possible if breeders choose to go outside of the color breeding "rules" but none are showable.

I don't know why, other than apparently GD breeders collectively decided they didn't like those colors/patterns in their breed.

Pretty much the bolded.
The only showable colors are fawn, brindle, black, blue, harle and mantle.

__________________

"We become better trainers by refusing to swallow uncritically what is tossed to us as truth,
by developing our powers of empathy and observation,
and by searching for better ways to teach and educate the dogs we love."

Yes, I just totally took advantage of this thread to show off my danish mismarks

__________________

"We become better trainers by refusing to swallow uncritically what is tossed to us as truth,
by developing our powers of empathy and observation,
and by searching for better ways to teach and educate the dogs we love."

Yes, all harles are genetically merles which is why in europe they have begun allowing merles in the breed ring.

__________________

"We become better trainers by refusing to swallow uncritically what is tossed to us as truth,
by developing our powers of empathy and observation,
and by searching for better ways to teach and educate the dogs we love."

"Any Great Dane which does not fall within the above color classifications must be disqualified." I think Red was asking about things like blue brindle, blue fawn, harlequin with fawn, brindle, blue, etc patches. All are technically genetically possible if breeders choose to go outside of the color breeding "rules" but none are showable.

I don't know why, other than apparently GD breeders collectively decided they didn't like those colors/patterns in their breed.